This function sets light brightness. Intensity application: finalColor = surfaceColor * lightColor * lightIntensity * attenuation, intensity is scalar multiplier applied to light contribution. Intensity ranges: 0.0 = off (no light), 0.5 = dim (half brightness), 1.0 = normal (default brightness), 2.0 = bright (double brightness), 5.0+ = very bright (oversaturated, blown out). Use cases: (1) Normal lighting (1.0 for standard lights), (2) Dim lights (0.3-0.7 for ambient fill, background lights), (3) Bright lights (2.0-5.0 for sun, explosions, searchlights), (4) Flickering (animate intensity 0.8-1.2 for torches, candles), (5) Fading (lerp intensity to 0.0 for lights turning off). Common patterns: sunlight b3dLightIntensity(sun, 2.5), torch b3dLightIntensity(torch, 1.5), dim lamp b3dLightIntensity(lamp, 0.5), flicker intensity=1.0 + math.rnd(0.2) - 0.1. Typical usage: set intensity once during setup for fixed brightness, animate intensity over time for dynamic effects (flickering, pulsing, fading). Intensity vs color: intensity affects brightness without changing hue (white * 2.0 = brighter white, not different color), color affects hue (red vs blue), both multiply together. Over-saturation: high intensity can cause over-bright surfaces (values > 1.0 in final color), HDR rendering handles this correctly (bloom, tone mapping), LDR rendering clamps to 1.0 (loses detail). Default intensity: lights default to 1.0 if not set. Performance: O(1) setting (simple struct assignment, no rendering cost until next frame). Validation: prints error if invalid light handle or non-light entity. Related: b3dLightColor sets light color/tint, b3dLightRange sets attenuation distance (affects brightness falloff), b3dCreateLight creates light entity.